1. Field of the Invention
This invention relates to a mine support, e.g. a mine roof prop having a linearly moveable, and/or pivoting, end plate, e.g. a bearing plate, and more particularly, to a yieldable mine roof prop having a bearing plate mounted on one end of a threaded shaft with the other end of the shaft mounted in an end of the prop, or having a bearing plate pivotally mounted on the end of the prop, or pivotally mounted on the end of the threaded shaft.
2. Description of the Presently Available Technology
In general, a mine roof support system includes a plurality of yieldable props, each prop having one end supported on the mine floor and the other end engaging the mine roof, or two or more two yielding props connected to one another by a support cross member. The yieldable props presently available have an inner conduit slidably mounted into an outer conduit and held at a desired length by a clamp assembly used alone or in combination with a collapsible member or insert. Embodiments of clamping assemblies and collapsible members are disclosed in U.S. Pat. No. 7,134,810 B2, which patent is hereby incorporated by reference.
As is appreciated by those skilled in the art, as a compression load, e.g., a shifting mine tunnel roof or floor acts on an end of the prop, the inner conduit slides into the outer conduit. Although the props presently available are acceptable for mine roof support systems, there are limitations. For example, the force of the clamping arrangement that maintains the conduits in a fixed relationship to one another controls the load that the prop can take before it compresses. Because the props are usually manually set and the clamp assembly manually adjusted in the mines, there is a variation in the compressive load each prop can support before collapsing. The limitations of props with clamping assemblies, e.g. the variation in the compressive load is eliminated by using collapsible inserts, e.g. of the type disclosed in U.S. Pat. No. 7,134,810 B2, to carry the load instead of the clamping arrangements.
Although props having clamping arrangements and collapsible inserts eliminate the limitations of the props having clamping arrangements alone, they also have limitations. More particularly, in the instance when the mine roof or floor is not level, an uneven compressive load is applied to the engaging surface of the bearing plate and to the insert.
As can be appreciated by those skilled in the art, it would be advantageous to provide a prop for a mine roof support system that does not have the limitations of the presently available props.